The present invention relates to an antifriction composite system for a bearing part, such as a sliding bearing bushing, with a metallic backing and a functional coating which comprises an anti-friction top layer. Furthermore, the present invention relates to a bearing part with an antifriction composite system of this type.
A composite system of the above-described type is known for example from DE 10 2004 020 385 A1. Described there is a method for producing sliding bearing bushing which have a metal casing as the backing, provided on the outside with an anticorrosive layer, and have a sliding layer of plastic, an anticorrosive agent in powder form being mechanically applied to form the anticorrosive layer.
To produce the bushing by the method for the intended application, among the material systems that are used are those known by the name NORGLIDE®. These are material composites comprising in particular compounded PTFE films on a metal backing, for example in the form of a metal gauze or mesh, an expanded metal, for example bronze-based expanded metal, or a solid steel back, for example a cold-rolled strip. When used for the production of bearing elements—with machining sometimes required—the systems are intended to ensure a great load-bearing capacity, in particular pressure absorption, low coefficients of friction in the tribological system, wear resistance and a long service life as well as freedom from maintenance—even when exposed to dust and/or moisture.
The set of requirements imposed on bearing elements, as are used for example as bushing in the furniture industry, in mechanical engineering and in automobile construction, varies to some extent. In automobile construction, for example, Volkswagen AG is bound by the company standard TL 257 (December 2002), which relates to “PTFE composite film with metal” and in which composite systems of the type mentioned above are described—including the requirements imposed on them, such as tensile, compressive and flexural load-bearing capacity.
The presence of certain fillers, such as for example graphite, in an antifriction composite system also makes it possible to control the electrical conductivity of bearing elements, this conductivity being determined not only by the type of filler but also by the nature and size of a contact area between the bearing and the shaft, the material thickness and the effective surface pressure. The increased conductivity serves in this case in particular for prevention with regard to the possible occurrence of undesired electrical charges of the components.
Further requirements for composite systems of the type mentioned above may arise from the fact that mechanical resistance under alternating stress, shock absorption or sound isolation, in particular to prevent the occurrence of disturbing sound, are necessary or desirable for some applications.
The known antifriction composite systems have a series of disadvantages here, such as a complex production process, which is caused by the use of highly cost-intensive materials, for example thick-walled PTFE films, or by the necessity for chemical, galvanic or—as in the case of DE 10 2004 020 385 A1—mechanical treatment operations, which in some cases are highly time-intensive. Among the weaknesses, one in particular is that of inadequate resistance, in particular thermal resistance, of the adhesive that is used to laminate the functional coating onto the backing.
The present invention is based on the object of providing an antifriction composite system of the type mentioned above and a bearing part which are distinguished by a simple and low-cost method of production and which meet the aforementioned requirements, in particular with regard to resistance to alternating stress and shock as well as sound absorption.
This object is achieved for the antifriction composite system of the type mentioned above by the functional coating having an elastomer layer lying directly under the top layer. The bearing part according to the invention is provided with the antifriction composite system according to the invention.
The invention produces many advantages with respect to technical aspects of its production and application.
For instance, the properties of the elastomer, which are to a great extent freely determinable, such as for example its Shore hardness, allow a desired resilience under shock loading to be specifically set.
The formation of an intimate bond of the elastomer layer with the metallic backing which may be promoted by an adhesion promoting layer interposed—and the top layer with a friction-reducing effect makes it possible to dispense with the use of a customary adhesive, and consequently also increase the thermal resistance of the entire composite system according to the invention.
Similarly, the state of edges of a bearing part, such as a sliding bearing bushing, which is produced from the antifriction composite system according to the invention can be improved—in particular with the effect that more efficient protection against substances with a delaminating effect getting under the top layer is achieved.
Apart from improved sound isolation, with the invention it is also possible if need be to set a desired, variably increased electrical conductivity or coloration.
A variation that is possible in the μm range of all the layers located on the backing, it being possible in particular for the top layer to be a layer containing a plastic or a plastics compound that comprises a polymer as the main constituent, particularly a fluorine-containing polymer, such as PTFE, allows dimensions that will produce exact fits to be set without the use of machining.
Finally, it is advantageously possible to produce an antifriction composite system by using the coil-coating method, i.e. a continuous and therefore comparatively less complex process, because the layer structuring according to the invention allows rolling up into a roll and unrolling from a roll to be ensured without damage—both in intermediate production steps and in the final state.